Organic Light Emitting Diodes (OLEDs) are considered to have wide application prospect in flat-panel display products due to their advantages such as self-emission, all-solid state, wide visual angle, quick response and the like. OLED displays have been regarded as the new generation of flat-panel displays since liquid crystal displays and plasma displays. Currently, OLEDs have been widely applied in the fields of both display and illumination. To ensure relatively high functional reliability and relatively low power consumption of a semiconductor light-emitting device in an OLED, external quantum efficiency of the semiconductor light-emitting device itself needs to be maximized.
In general, the external quantum efficiency of a semiconductor light-emitting device depends on internal quantum efficiency and light extraction efficiency (LEE) thereof. Since the internal quantum efficiency is decided by the characteristics of the material itself, it is particularly important to improve the light extraction efficiency under the condition that the internal quantum efficiency cannot be improved effectively. Improving the light extraction efficiency is to introduce as much light emitted from inside the OLED as possible to the outside of the semiconductor light-emitting device.
As shown in FIG. 1, an existing OLED array substrate includes a substrate 1 on which thin film transistors (not shown) are provided, and OLED units controlled by the thin film transistors on the substrate 1, and a typical OLED unit comprises an anode 2, an organic light-emitting layer 3 and a cathode 3 which are sequentially arranged. For a top-emitting OLED array substrate, as the cathode 4 is generally a semi-transparent metal electrode, reflection of light emitted by the organic light-emitting layer 3 at this electrode may increase, which leads to interference among multiple photon beams, and results in obvious microcavity effect (a phenomenon of different intensity and wavelength of light at different emission angle due to optical interference inside the device). Therefore, when a display comprising such top-emitting OLED array substrate is used, density and color of emitted light may change with the visual angle.
In the prior art, in order to attenuate the microcavity effect, an optical coupling layer 5 may be coated on the cathode 4, and material for forming the optical coupling layer 5 has a refractive index larger than that of material for forming the cathode 4, in other words, the refractive index of the optical coupling layer 5 is larger than that of the cathode 4. Experiments showed that when the refractive index of the optical coupling layer 5 (the refractive index of the optical coupling layer 5 is generally larger than 2.0) is larger than those of the organic light-emitting layer 3 and the cathode 4, transmittance of the cathode 4 increases, and increase in the transmittance of the cathode 4 will attenuate the microcavity effect.
In the prior art, a open type mask is usually applied to form the optical coupling layer 5 by evaporation, that is, evaporation are performed on all OLED units at the same time to form an uniform-thickness type optical coupling layer 5 as shown in FIG. 1. However, as the refractive index of the optical coupling layer 5 is relatively high, and is usually larger than that of a gas blanket outside the optical coupling layer 5, for example, is larger than that of a nitrogen blanket, which results in total reflection inside the uniform-thickness type optical coupling layer 5, thus a part of light intensity is lost and the light extraction efficiency is lowered.